The invention relates to a drive for a moveable jaw of a machine vice, comprising a screw spindle and a power amplifier operable by means of a crank, the drive, which is arranged beneath the clamping plane of the jaws, being supported by means of an annular flange on a thrust block at one end of the vice body, on whose other end the fixed jaw is arranged, and the screw spindle engaging into a spindle nut of the moveable jaw.
A machine vice of the general type described above is described in German patent specification No. 3,437,403 and comprises a fixed jaw which is arranged at one end on a vice body and a moveable jaw which is arranged at the other end. The drive consists of a power amplifier which acts on a screw spindle. The arrangement is made in such a way that the crank is located on one side, the crank acting on the power amplifier on the other side of the thrust block. During the crank movement the moveable jaw is first advanced via the screw spindle, and a workpiece is clamped with a predetermined force. If this force or the torque applied at the crank is exceeded, a coupling disengages and the power amplifier comes into effect and exerts pressure on the screw spindle in the axial direction, which acts on the moveable jaw via a slide. In this way, a workpiece can be clamped with high force into the machine vice, and in particular this makes it unnecessary for very high torques to be transmitted via the thread turns of the threaded spindle, which would considerably limit the service life of the latter.
A power amplifier as is used in the above-mentioned machine vice has been disclosed, for example by German patent specification No. 2,308,175.
U.S. Pat. Nos. 3,397,880 and 4,043,547 have disclosed a machine vice which, with regard to the arrangement of the spindle, the crank, the thrust block and the two jaws, is similar to the machine vice above but the machine vices described do not have a power amplifier. The clamping force is applied solely by the screw movement of the spindle and to clamp the workpieces adequately in position, considerable forces have to be applied to the screw spindle which leads to rapid wear.
It is advantageous in this type of vice that the screw spindle is located below the mounting plane for the workpieces so that it is possible to use a relatively small overall length, since the overall length of the drive is not added to the opening capacity and the jaw dimensions, and it is also possible to exert a downward pull on the moveable jaw which counteracts the yawning of the jaws under the clamping pressure. Furthermore, the construction in which the slide is arranged with essential parts beneath the clamping jaws and is surrounded by the machine body is very robust.
In German Auslegeschrift 1,288,523 a machine vice is described in which the screw spindle is arranged inside the moveable jaw. The thrust block is also accommodated inside the moveable jaw, and the entire drive is located above the clamping plane. In this construction, provision is made for a power amplifier outside the moveable jaw, the power amplifier then acting on the moveable jaw via the screw spindle. In this construction, the vice, together with its parts is adapted to the drive from the outset. A considerable overall length also results, since the overall length of the drive is added to the other dimensions in the retracted position.